Climate Change - page 2

Polar Regions and Climate Change

In a remote Eskimo village on the edge of the Arctic Ocean, residents are feeling the effects of warming temperatures. For thousands of years, the native Inupiat people have lived in the vicinity that is now Kaktovik, surviving on subsistence hunting of both marine and land animals.

Now, much of the ice that has defined their existence for so long is melting. Coastlines are eroding, and polar bears - which typically live and hunt on sea ice - are now turning up on land as the ice retreats farther from shore each year.

In the past 30 years, both the Arctic and Antarctica have shown signs of rapid change.
Satellite data have revealed a dramatic reduction in Arctic sea ice extent in recent years. In September 2005, the mean sea ice extent dropped to about 5.3 million square km (2.1 million square miles) - the lowest recorded since satellites began taking measurements in 1978.

Warmer temperatures can also destabilize the fragile balance between ice shelves and the glaciers that feed them. When temperatures heat up, glacier flow speed increases and can lead to the disintegration of an ice sheet. In the 18 months following the 2002 breakup of the Larsen B ice shelf, adjacent glaciers on the Antarctic Peninsula flowed at up to eight times their normal speed. Also in 2002, the Ward Hunt ice shelf on the coast of Ellesmere Island in northern Canada broke up, after a century-long decline in the ice shelf's extent.

This RADARSAT image shows the central crack in the Ward Hunt Ice Shelf. The ice shelf, which was located off the coast of Ellesmere Island in northern Canada, broke up in September 2002. (Image credit: Alaska Satellite Facility, Geophysical Institute, University of Alaska Fairbanks)

Recent analyses of climate model results indicate that in the Northern Hemisphere, warming temperatures may cause up to half of the top 3 meters (10 feet) of permafrost to thaw. Permafrost is perennially frozen ground that occurs where the temperature remains below 0 degrees C (32 degrees F) for several years. Thawing permafrost can alter ecosystems and damage buildings and roadways across Canada, Alaska, and Russia. In addition, since carbon dioxide and methane are stored in permafrost soil, thawing permafrost could release large amounts of these greenhouse gases into the atmosphere, beyond the amounts already produced by human activities, such as the burning of fossil fuels, deforestation, and intensive agriculture.

The terminus of the Lamplugh Glacier in Glacier Bay, Alaska, has advanced more than a third of a mile since 1941. (Image credit: Bruce Molnia, U.S. Geological Survey)

Other recent changes in the Northern Hemisphere include earlier spring breakup of river ice, vegetation changes in tundra regions, and shrinking glaciers. More than 100 glaciers have disappeared from Glacier National Park in Montana during the past 150 years. The Global Land Ice Measurements from Space (GLIMS) project is an international effort to develop an inventory of the world's glaciers. By comparing current satellite data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument with historic photos and maps, scientists can detect changes in glacier size and movement.

This image from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument shows the lakes left behind by retreating glaciers in the Bhutan-Himalaya. The rapid growth of lakes on glacier surfaces in the Himalaya indicates that glaciers in that region are retreating at alarming rates. (Image credit: Jeffrey Kargel, USGS/NASA JPL/AGU)

On a geologic time scale, however, all of these trends have occurred in a short time period when compared to the Earth's natural cycles of temperature variability. For example, the increase in global temperature from the last ice age to the current interglacial period was about 5 degrees C (just under 3 degrees F), which is similar to the temperature increase for the 20th and 21st (projected) centuries alone. Many studies are underway to help researchers understand what the current trends mean to the global climate system and biosphere.

Climate on Mars

Scientists are only beginning to study the climate history of Mars. Geological evidence of ancient water erosion suggests that Mars was perhaps once a warmer planet. But for the most part, the climate history of Mars is still a mystery.

This Mars Orbiter Camera (MOC) image shows layers of sedimentary rock in a crater in the western Arabia region of Mars. Scientists believe the existence of distinct layers suggests that climatic conditions have changed over the entire planet from time to time. (Image credit: NASA/JPL/Malin Space Science Systems)

One thing that most researchers agree on, however, is that Mars has undergone periods of dramatic climate change throughout its geologic history, and some evidence indicates that Mars is currently in a period of rapid change. The holes in the "swiss cheese" landscape at the southern polar region, which are formed when ice sublimes at different rates, have grown larger within the past several years, based on satellite imagery.

Unlike Earth, whose axial tilt is kept fairly stable by forces associated with the Moon, Mars' axial tilt has varied from as low as 13 degrees to as high as 40 degrees over the last few million years. These variations in tilt would have caused extreme changes in seasonal climate from one period to another, possibly including episodes of melting ice and water production. Calculations show that throughout Mars' geologic history, its average axial tilt would have been about 40 degrees, unlike the present 25.2 degrees, and sometimes the tilt could have reached as high as 80 degrees. During periods of very high tilt, ice would accumulate in the tropics rather than at the poles.

In the south polar region of Mars, mesas and circular depressions formed mostly from frozen carbon dioxide reveal layers that hint at a previously colder Martian climate. (Image credit: NASA/JPL/Malin Space Science Systems)

In Earth's polar regions, scientists can drill deep into the ice for core samples that reveal different layers of deposits. By analyzing these layers, researchers can tell what the climate was like when the layer was deposited. For example, the contents can reveal whether a volcanic eruption occurred during a certain time period, and air bubbles in the ice core can indicate what the composition of the atmosphere was at the time the air was trapped.

Similarly, Mars' polar regions have the potential to reveal much about the planet's climate history. The layered deposits that underlie the Martian ice caps could hold a wealth of information about the nature of climate change on Mars.

Phoenix will land during the retreat of the Martian polar cap, when cold soil is first exposed to sunlight after the long winter. The interaction between Mars' ground surface and atmosphere that occurs at this time is critical to understanding Martian climate. Phoenix will gather data about this interaction and other surface meteorological conditions, serving as the first weather station in the Martian polar region. Data from this station will significantly improve models of global climate on Mars.